QML console.log() and console.debug() don't write to console

Question

I'm using Qt 5.6 on Fedora 23 and I noticed that console.log() and console.debug() don't write anything to console. My example code:

import QtQuick 2.6
import QtQuick.Window 2.2

Window {
    visible: true

    Text {
        text: qsTr("Hello World")
        anchors.centerIn: parent

        Component.onCompleted: {
            console.warn("warn completed")
            console.log("log completed")
            console.error("error completed")
            console.debug("debug completed")
            console.exception("exception completed")
            console.info("info completed")
        }
    }
}

prints to console:

QML debugging is enabled. Only use this in a safe environment.
qml: warn completed
qml: error completed
qml: exception completed
onCompleted (qrc:/main.qml:16)
qml: info completed

so warn, error, exception, and info work fine. What am I doing wrong?

Edit #1: Project is freshly created, all my sources:

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

project.pro

TEMPLATE = app

QT += qml quick
CONFIG += c++11

SOURCES += main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Default rules for deployment.
include(deployment.pri)

Edit #2: Compile Output from Qt Creator shows that there are no QT_NO_DEBUG_OUTPUT, QT_NO_INFO_OUTPUT, or QT_NO_WARNING_OUTPUT:

14:43:36: Running steps for project project...
14:43:36: Configuration unchanged, skipping qmake step.
14:43:36: Starting: "/usr/bin/make" 
g++ -c -pipe -g -std=gnu++0x -Wall -W -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_QUICK_LIB -DQT_GUI_LIB -DQT_QML_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -I../project -I. -I../../Qt5.6.0/5.6/gcc_64/include -I../../Qt5.6.0/5.6/gcc_64/include/QtQuick -I../../Qt5.6.0/5.6/gcc_64/include/QtGui -I../../Qt5.6.0/5.6/gcc_64/include/QtQml -I../../Qt5.6.0/5.6/gcc_64/include/QtNetwork -I../../Qt5.6.0/5.6/gcc_64/include/QtCore -I. -I../../Qt5.6.0/5.6/gcc_64/mkspecs/linux-g++ -o main.o ../project/main.cpp
/home/krzys/Qt5.6.0/5.6/gcc_64/bin/rcc -name qml ../project/qml.qrc -o qrc_qml.cpp
g++ -c -pipe -g -std=gnu++0x -Wall -W -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_QUICK_LIB -DQT_GUI_LIB -DQT_QML_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -I../project -I. -I../../Qt5.6.0/5.6/gcc_64/include -I../../Qt5.6.0/5.6/gcc_64/include/QtQuick -I../../Qt5.6.0/5.6/gcc_64/include/QtGui -I../../Qt5.6.0/5.6/gcc_64/include/QtQml -I../../Qt5.6.0/5.6/gcc_64/include/QtNetwork -I../../Qt5.6.0/5.6/gcc_64/include/QtCore -I. -I../../Qt5.6.0/5.6/gcc_64/mkspecs/linux-g++ -o qrc_qml.o qrc_qml.cpp
g++ -Wl,-z,origin -Wl,-rpath,\$ORIGIN -Wl,-rpath,/home/krzys/Qt5.6.0/5.6/gcc_64/lib -o project main.o qrc_qml.o   -L/home/krzys/Qt5.6.0/5.6/gcc_64/lib -lQt5Quick -lQt5Gui -lQt5Qml -lQt5Network -lQt5Core -lGL -lpthread 
14:43:37: The process "/usr/bin/make" exited normally.
14:43:37: Elapsed time: 00:01.

Answer 1

Fedora 22 and later disables Qt debug output by default [1]. You can enable Qt debug output by modifying the system-wide /etc/xdg/QtProject/qtlogging.ini or by creating a user-specific configuration file ~/.config/QtProject/qtlogging.ini for example with the following contents:

[Rules]
*.debug=true

1. https://bugzilla.redhat.com/show_bug.cgi?id=1227295

Answer 2

I found a more convenient solution by adding one of the two - depending on if you use Qt Quick 1 or 2 to the pro file (rebuild and run QMake again) according to https://doc.qt.io/qt-5/qtquick-debugging.html:

Qt Quick 1: CONFIG+=declarative_debug
Qt Quick 2: CONFIG+=qml_debug

To put it in your code it would look like:

project.pro

TEMPLATE = app

QT += qml quick
CONFIG += c++11 qml_debug #or CONFIG+=declarative_debug for QtQuick 1

SOURCES += main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Default rules for deployment.
include(deployment.pri)

Now it might look like this:

Answer 3

Instead of enabling Debug logging system wide like jpnurmi suggests in the accepted answer. You can simply set a system variable to get the debug messages to show up in the console. Qt Wiki about Logging Rules

To set it for one single execution of your app or qmlscene/qhot qml-preview. If you are starting them from the commandline:

$ QT_LOGGING_RULES="*.debug=true; qt.*.debug=false" your_executable
$ QT_LOGGING_RULES="*.debug=true; qt.*.debug=false" qmlscene/qhot main.qml

Or to set it for this session only (will be unset after reboot). And should be respected even if you launch/test from QtCreator or other IDE:

$ export QT_LOGGING_RULES="*.debug=true; qt.*.debug=false"

And then just start/test your executable or qmlscene/qhot normally

Why is this better?

Setting the logging rules systemwide will mean all Qt apps you run will write debug messages to their logfiles. I discovered a few log files that were gigabytes in size because the apps were accumulating a huge amount debug messages in their logs during normal usage.